Several techniques for locating wireless devices involve the Mobile Station (MS) making measurements of the signals transmitted by the base stations of a wireless communication network. (The term MS or Mobile Station, as used herein, refers to any type of wireless phone or other mobile device having a radio communications capability.) These techniques are known by the acronyms EOTD, AFLT, OTD and ECID.                Enhanced Observed Time Difference (EOTD) is a location technique defined in the ETSI 3GPP Technical Specification 43.059 in which a GSM MS makes relative time difference measurements of the beacon signals transmitted by geographically distributed base stations, where these measurements are used to compute a position.        Advanced Forward Link Trilateration (AFLT) is a technique defined in the TIA IS-95 and CDMA 2000 standards in which a CDMA MS makes relative time difference measurements of the pilot signals transmitted by geographically distributed CDMA base stations, where these measurements are used to compute a location.        Observed Time Difference (OTD) is a location technique defined in the ETSI 3GPP Technical Specification 23.271 in which the User Equipment (UE), which is essentially a mobile station in a UMTS network, makes relative time difference measurements of the signals transmitted by geographically distributed Node Bs (base stations in a UMTS system), where these measurements are used to compute a location.        Enhanced Cell Identification (ECID) is a technique used to locate GSM MSs in which the MSs perform received power level measurements of the signals transmitted by geographically distributed GSM base stations, where these measurements are used to compute locations.        
All of these location techniques involve a MS measuring signals whose characteristics vary as a function of the distance between the MS and the Base Stations transmitting the signals. In addition, all of these location techniques require knowledge of key cell site information. Such key cell site information may include cell identification information and transmit antenna location. In addition, some of these location techniques require additional information about the transmitters, such as transmitter signal timing, signal transmit power, and signal propagation or signal loss in the environment. This information can be difficult to obtain from wireless network operators because it is dynamic and distributed across multiple data bases. This information may be difficult to obtain and maintain across multiple wireless network operators, as some operators may not be willing to cooperate and provide this information. The accuracy of each of the location techniques described above will be improved if a larger number of the base station signals are used in the location solution, which is possible when the transmit signals across multiple wireless networks are available. The accuracy of each of these techniques is dependent upon the number and quality of the signals available for measurement, and so the ability for a location solution to utilize these signals across multiple wireless networks will provide better performance than could be achieved if the measurements were limited to the signals of a single wireless network.
The subject matter described herein provides an automatic way to detect the existence of one or more useful wireless transmitters, determine the cell identification information so that each transmitter can be referred to later, determine the transmitter antenna locations, determine the transmitter timing, determine the transmitter power level, and determine the signal power loss as a function of location, so that any such wireless transmitter can be used to locate mobile stations.
Additional Background Information Relating to Subscriptionless Location
The location of the MS is done by combining the measurements made by the MS of the downlink base station transmit signals, with the cell site information. This can be done either in the MS, or within the network, but in either case this involves the transfer of the cell site information and/or the MS measurements to the node which computes the location. In the systems deployed today, this information is transferred by the wireless link provided by the same wireless network that provides the downlink transmit signals upon which the location estimate is based. This could be either a control plane connection or a user plane connection. (See application Ser. No. 11/533,310, filed Sep. 19, 2006, “User Plane Uplink Time Difference of Arrival (U-TDOA),” for a description of a user plane approach to network-based wireless location. As described, in a user plane architecture, a location server can communicate directly with the mobile device via a data or IP (Internet Protocol) link carried by the wireless operator's radio network but not part of the control/voice (or access/traffic) channel structures, thus requiring no modifications to the core or radio network.) These techniques, however, do not support devices which are not served by the wireless network that is providing the downlink signals on which the location estimate is based. These techniques require that the device support two-way communication with the wireless network, and therefore require hardware in the device to support transmission to the wireless network. In addition, these techniques require utilization of the wireless network resources, as well as permission from a wireless service provider to facilitate the location. A system is needed to allow devices that are not able or allowed to communicate with the wireless network to be located based on measurements of downlink transmit signals provided by the wireless network. Many devices existing today that need to be located normally have data connections to the Internet (e.g., through Ethernet, broadband service providers using cable, fiber optics, or DSL, PSTN dialup connections, or 802.11 WiFi connections). By adding a wireless receive only capability to these devices to make measurements of the existing wireless downlink signals, the data connection can be used to provide a link between the device and location server to facilitate location. The devices, for example, could include desktop or laptop computers, voice over IP (VoIP) devices, or WiFi access nodes.
A goal of the invention described herein is to provide a way to locate devices based on downlink signal measurements made by the devices, where the devices are not part of the wireless network or are not provided wireless service by the network. (As used herein, an expression such as based on [certain measurement/information] is not intended to mean that only the recited information or measurements are used. This expression should be given a broad meaning such that, for example, the wireless device may be located using the recited measurements in addition to other information.) Another goal is to provide a way to locate devices based on downlink signal measurements made by the devices, where the devices do not possess the ability to transmit signals to the wireless network. Yet another goal is to provide a way to locate devices based on downlink signal measurements made by the devices, where communication resources of the wireless network are not consumed to facilitate location.